1. Field of Invention
The present invention relates generally to the fabrication of semiconductor devices such as light-emitting devices in misfit systems. In particular, the lattice defects are guided to and contained in designated locations defined by textured districts on the substrate surface. As a result, the free propagation of extended defects through the active region is restricted and the overall defect density of the system is reduced.
2. Description of Prior Art
Lattice-mismatched system such as GaAs/Si is promising to obtain large-area wafers for optoelectronic device applications. However, the quality of the directly disposed layer is inferior due to the penetration of threading dislocations in this material system. M. Akiyama et al demonstrated GaAs layer on Si substrate the using a low-temperature buffer layer and a superlattice intermediate layer in U.S. Pat. No. 4,561,916.
Seeded overgrowth has also been used as an alternative to obtain single crystalline epilayers deposited over the surface of an amorphous mask layer. In the context of epitaxial lateral overgrowth (ELO), the seed layer extends through the apertures and spreads over the mask surface. The building block of the prior art ELO method is the selective epitaxial growth (SEG) where no nucleation takes place on the mask surface. B. D. Joyce et al reported SEG of Si epilayer over the oxide mask using chemical vapor deposition (CVD) in Nature, Vol. 195 (1962) pp. 485-486. F. W. Tausch, Jr. et al demonstrated GaAs on SiO2 mask using ELO in J. Electrochem. Soc. Vol. 12 (1965) pp. 706-709. The ELO method has been used to fabricate silicon-over-insulator (SOI) using CVD as described by L. Jastrzebski et al in J. Electrochem. Soc. Vol. 130 (1983) pp. 1571-1580 and by J. F. Corboy, Jr. et al in U.S. Pat. No. 4,578,142.
The ELO method has also been used to deposit GaAs epilayers on Si substrate by Y. Ujiie et al in Jpn. J. Appl. Phys. Vol. 28(3) (1989) pp. L337-L339. Thus a GaAs layer is first grown on the Si(11) substrate using molecular beam epitaxy. A SiO2 mask is formed on the GaAs surface by photolithography and the GaAs layer is deposited using liquid phase epitaxy. The defect density is reduced in the overgrown layer where the threading dislocations are blocked by the mask layer. Similarly, A. Usui et al described the ELO growth of GaN on sapphire using hydride vapor phase epitaxy (HVPE) in Jpn. J. Appl. Phys. Vol. 36 (1997) pp. L899-L902. R. F. Davis et al described the ELO growth of GaN layer on SiC substrate in U.S. Pat. No. 6,051,849. The influence of the substrate can be further reduced by making the ELO layer suspended above the substrate as described by S. Kinoshita et al in J. Crystal Growth, Vol. 115 (1991) pp. 561-566 and by K. J. linthicum et al in U.S. Pat. No. 6,177,688.
The prior art methods have following drawbacks. The layer growth from the mask openings allows for the free propagation of dislocations into the active layer. As a result, multiple ELO steps are required for defect reduction causing long cycle time and poor process yield. This restraint can be relaxed somewhat by depositing the layers over etched surface features with a specific inclination angle. However, the layer disposition over prescribed surface feature is highly sensitive to the etching defects. The etching defects expose random nucleation sites causing adverse micro-faceting and layer deterioration. Thus structural defects are inevitably generated as the growth front attempts to negotiate surface defects with sharp corners and abrupt changing curvature. The grown-in defects will multiply and propagate into the active region during operation causing premature degradation of the device. These drawbacks offset the benefits of using the ELO method for defect reduction.